Anisotropic compression and trigger-bond identification in a fused heterocyclic energetic crystal under high pressure up to 10 GPa.

CONTEXT: The fundamental challenge in designing advanced energetic materials lies in optimizing the balance between high performance and low sensitivity. This work employs periodic density functional theory to probe the behavior of 6-amino-9,10-dinitropyrazolo[1,5-d] [1-3] triazolo[3,4-f][1,2,4]triazin-3(2H)-one under hydrostatic pressures up to 10 GPa. The computational model is rigorously validated against experimental lattice parameters and infrared spectra. Under compression, the crystal exhibits strongly anisotropic lattice contraction, most pronounced along the c-axis. Analysis reveals a concomitant strengthening of key intralayer N-H…O=N hydrogen bonds and a reduction in interlayer spacing governed by van der Waals interactions. The aromaticity of the fused pyrazole, triazole, and triazine rings is systematically enhanced with pressure. Combined frontier orbital and Laplacian bond order analyses consistently identify the N-H bond within the triazole ring as the weakest structural link, indicating its cleavage as the probable initial decomposition step. We propose a detailed initiation pathway involving pressure-facilitated intermolecular hydrogen transfer, followed by triazine ring-opening and NO2 release. These findings provide crucial atomistic insights into the stability and reactivity of this material under extreme conditions, informing its safe handling and potential application.

METHODS: The CP2K software package was employed to carry out periodic DFT calculations. Exchange-correlation effects were described using the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation, together with the D3 (BJ) empirical dispersion correction. Core electrons were represented by GTH pseudopotentials, while the valence electrons were modeled with the DZVP-MOLOPT-SR-GTH basis set. A plane-wave energy cutoff of 400 Ry was adopted. For each target pressure (spanning from 1 atm to 10 GPa), structure optimizations used the BFGS algorithm under tight convergence thresholds for forces, displacements, and stress. Infrared spectra were derived from vibrational analysis on optimized structures. Electronic structure analysis was performed using the Multiwfn software. For example, The IGMH analysis was then performed using the Multiwfn program (version 3.8, running on Windows) with an isovalue of 0.015 a.u. and default grid spacing. The resulting isosurface grid (cube) files were visualized using VMD software.